#13572: Add ArgMin / ArgMax pattern synonyms -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: feature | Status: new request | Priority: normal | Milestone: Component: | Version: 8.0.1 libraries/base | Keywords: | Operating System: Unknown/Multiple PatternSynonyms | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- {{{#!hs import Data.Semigroup pattern ArgMin :: a -> b -> ArgMin a b pattern ArgMin a b = Min (Arg a b) pattern ArgMax :: a -> b -> ArgMax a b pattern ArgMax a b = Max (Arg a b) }}} Or even record pattern synonyms, à la [https://github.com/energyflowanalysis/efa-2.1/blob/3eb86c0b6b2d2fb66cd5b76ce... this] {{{#!hs pattern ArgMin :: a -> b -> ArgMin a b pattern ArgMin {minArg, minValue} = Min (Arg minArg minValue) pattern ArgMax :: a -> b -> ArgMax a b pattern ArgMax [maxArg, maxValue} = Max (Arg maxArg maxValue) }}} and we can define {{{#!hs import Data.Semigroup.Foldable argmin :: Ord k => Foldable1 f => (a -> k) -> (f a -> a) argmin f = minValue . foldMap1 (\a -> ArgMin (f a) a) argmax :: Ord k => Foldable1 f => (a -> k) -> (f a -> a) argmax f = maxValue . foldMap1 (\a -> ArgMax (f a) a) }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13572 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler